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marucs13 Group Title

Why do some law of sines problems have none or two solutions?

  • 4 months ago
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  1. starrhunter Group Title
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    Because a number canbe positive or negative and still result in the same outcome in a law of sines problem.

    • 4 months ago
  2. Kaederfds Group Title
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    and it can be has more than 2 solutions too

    • 4 months ago
  3. marucs13 Group Title
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    can you explain better please...

    • 4 months ago
  4. Kaederfds Group Title
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    because sin has periodic

    • 4 months ago
  5. jim_thompson5910 Group Title
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    This page may help you out http://www.regentsprep.org/Regents/math/algtrig/ATT12/lawofsinesAmbiguous.htm

    • 4 months ago
  6. soccergurl978 Group Title
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    because it depends on the quadrant of which the equation puts it. for example, sin is positive in the first and second quadrant (ASTC).. if your number is positive then it would be in quadrants I & II. if your number is negative then it would be in quadrants III & IV

    • 4 months ago
  7. marucs13 Group Title
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    jim do you agree with soccergurls answer?

    • 4 months ago
  8. jim_thompson5910 Group Title
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    yes, ATSC is an acronym that refers to you going from quadrant I to quadrant IV A: all are positive in quadrant 1 (sine, cosine, tangent) S: only sine is positive in quadrant 2 T: only tangent is positive in quadrant 3 C: only cosine is positive in quadrant 4 also, sine is positive for quadrants 1 & 2

    • 4 months ago
  9. jim_thompson5910 Group Title
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    and as the page I posted points out, sometimes you'll get something like sin(C) = 1.1428 but sin(x) is restricted from -1 to +1, which means sin(C) = 1.1428 has no solution and therefore, a triangle is not possible

    • 4 months ago
  10. marucs13 Group Title
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    ah, i think i get it now, thank you :)

    • 4 months ago
  11. jim_thompson5910 Group Title
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    yw, the page also goes over other examples too (of the 2 other cases)

    • 4 months ago
  12. marucs13 Group Title
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    okay, thank you :)

    • 4 months ago
  13. marucs13 Group Title
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    umm can i ask a follow up question...?

    • 4 months ago
  14. marucs13 Group Title
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    why does law of cosines not have any ambiguous cases?

    • 4 months ago
  15. jim_thompson5910 Group Title
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    To have an ambiguous case, it means that you aren't sure of what the angles are (if all the sides are known). Let's say we know the lengths of all 3 sides of two triangles. Furthermore, let's say that the corresponding lengths are congruent. If that's true, then we can use the SSS property to show that the two triangles are congruent. Now the question is: is it possible to have 2 congruent triangles but have one set of corresponding angles that are incongruent (of different measures)? The answer is no. The reason is the CPCTC property tells us that if we have congruent triangles, then the corresponding parts will be congruent as well. So the corresponding angles will be congruent, which means knowing all 3 sides leads you to find all 3 angles without any ambiguity or confusion. You can find any angle of a triangle using the law of cosines a^2 = b^2 + c^2 - 2bc*cos(A) where a,b,c are the sides and A,B,C are the angles (angle A is opposite side a, etc etc). So if you know a,b,c then A will be one fixed value and there won't be any ambiguity. This is true for B,C as well.

    • 4 months ago
  16. jim_thompson5910 Group Title
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    Unfortunately, if you're dealing with SSA, then you may run into ambiguity. This is because knowing two sides and the angle that's not between them doesn't uniquely determine a triangle (think back to geometry). So what this means is that if you were to plug in the sides and angle into a^2 = b^2 + c^2 - 2bc*cos(A), you would get a quadratic which has the potential to a) have 2 different solutions b) have exactly one solution c) have no solutions at all so the ambiguity still creeps up. But again, this is only possible if working with SSA

    • 4 months ago
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